This will almost certainly be my last Billion router. They have awful support
and refuse to respond to simple questions about failing hardware, but for now,
I’m persevering with the Billion 7800VDOX modem/router because that’s what I have.
The O series of routers comes with a VPN server built in (either PPTP or
L2TP), but since PPTP is inherently insecure now, I’m setting up L2TP over
IPSec and having this work with my iOS device. I’d managed to find a PDF
provided by Billion about this a while back, but could no longer find it …